Window doesn't resize when opening new animation

[cibomahto]

When an animation is opened that is larger than can be shown in the current window, it remains hidden until the user makes the window longer

Platform: OS X (but should affect all)

Steps to reproduce:
-Open a long animation

[cibomahto]

It's actually not clear that this is the right way to handle it. Instead, a scroll bar should probably show up under the animation, and allow you to move back and forth across it. Closing and opening a new issue reflecting this.